Various means have been used in the prior art to function a gyroscopic rate switch. In the past the rotor of the gyroscopic switch was run-up and maintained at constant speed by the use of an electric motor. The prior art devices using electrically driven rotors have been unsatisfactory because of the difficulty in bringing the rotor speed up to a constant value in less than 0.4 seconds and for maintaining it constant for a period of more than 10 seconds without the use of relatively large size heavy auxiliary batteries. Guided missiles, using the aforementioned prior art rate switches for determining spin rate, have had to sacrifice valuable warhead size and reduced lethality because of the necessity of carrying an external power source for the operation of the gyroscope.